1. Field of the Invention
This invention relates to a resinous composition possessing a rubber-like elasticity which comprises a vinyl chloride polymer and a thermoplastic polyurethane formed by reacting an organic diisocyanate with a polyester diol obtained by reacting a polyol component comprising 1,6-hexanediol and a low molecular weight diol having a side-chain methyl group, with a saturated aliphatic dicarboxylic acid having 5 to 8 carbon atoms.
2. Description of the Prior Art
Thermoplastic polyester-urethanes (for example, Estane 5740-070 or 5470-010, commercially available from B. F. Goodrich Chemical Co.) have excellent physical properties such as high abrasion resistance, high solvent resistance and high toughness and they can provide rubber-like elastomeric materials that do not require vulcanization. However, they have disadvantages owing to the autoxidation sensitivity of the urethane linkage, such as inferior weatherability and heat resistance. Further, they are more expensive than other commercial thermoplastic resins ordinarily used in various fields.
These disadvantages can be overcome by blending into such thermoplastic polyester urethanes suitable amounts of inexpensive vinyl chloride resins which are excellent in weatherability and heat resistance, but molded articles prepared from such conventional polymer blends exhibit no rubber-like elasticity.
The relation between the bound resilience, R, used as an index of the rubber-like elasticity, and the mechanical loss tangent, tan .delta., used as an index of the polymeric structure, is represented by the following formula (Journal of Japanese Rubber Association, Volume 39, No. 9, pages 665-673, 1966; Rubber Test Methods, 1963 compiled by the Rubber Association): EQU R/100 = exp(-.pi.tan .delta. )
Namely, the smaller is the value of tan .delta., the larger is the value of the bound resilience.
The rubber-like elasticity is manifested by the formation of a cross-linked network structure by chemical linkages or strong physical pseudo-linkages in a polymer main chain in the non-frozen state. Accordingly, in order for a polymer to manifest a suitable rubber-like elasticity, it is indispensable that the glass transition temperature of the polymer should be much lower than practical application temperatures and that the value of tan .delta. at practical application temperatures should be extremely small.
In view of the foregoing, it is considered that in order for a blend comprising a polyester-urethane and a vinyl chloride polymer to have a low glass transition temperature, it will be preferred to use a polyester-urethane composed of recurring units having an average carbon number which is as large as possible. As a result of our experiments, however, it was confirmed that no tendency of reduction of the glass transition temperature is brought about by increasing the weight average carbon atom number, and it was found that if the limit of compatibility between the polyester-urethane and the vinyl chloride polymer is exceeded, the glass transition temperature increases and a product having a desirable rubber-like elasticity cannot be obtained. Further, when, in order to establish a glass transition temperature as low as possible, a symmetric linear polyester-urethane was synthesized while avoiding introduction of side chains, which were considered to bring about adverse effects, and the thus-synthesized polyester-urethane was blended in a vinyl chloride polymer, it was found that the low elongation modulus of a molded article prepared from the above composition increased with the passage of time and it became rigid and hard with increase of the glass transition temperature and that the rubber-like elasticity was eventually lost.